The present invention relates to a rotary type pumping machine of the type in which compressed air is supplied into the machine to facilitate the starting up of the machine. More particularly, the invention is concerned with a rotary type water-lift machine of the type mentioned above, having an air discharging valve for discharging the compressed air introduced into the runner chamber.
Pumped storage hydro-electric plant is known as a power generating plant which is able to pump up the water to an upper reservoir of a certain height above a water turbine which in such a case operates as a pump driven by surplus electric power and generating electric power by making use of the water in the upper reservoir at the time of peak load. In the starting up of the large-size rotary type pumping machine used in this type of plant, it is an ordinary measure to introduce compressed air into the runner chamber to depress the water in the chamber to a predetermined level in the draft pipe to reduce the starting torque for starting the runner and, when the runner speed is increased to a predetermined speed, the air is discharged to commence the ordinary pumping operation.
In recent years, there is a demand for greater head and capacity in the field of the pumped storage hydro-electric plant. In addition, this type of hydro-electric plant is usually constructed as an underground plant. Therefore, the air and water discharged from various portions of the plant gather in a water collecting pit provided in the plant and are discharged therefrom by, for example, a water discharge pump.
According to this arrangement, however, there is a fear that the water overflows the water collecting pit and, in the worst case, the plant as a whole is flooded by the water, when the water discharge pump becomes inoperative due to, for example, a power failure in the plant or when the flowing rate of the water into the water collecting pit exceeds the capacity of the water discharge pump.
Particularly, in the pumped storage hydro-electric plant having an air discharge valve for discharging compressed air from the runner chamber, the water may flow back at a large rate from the draft pipe through the runner chamber to cause the overflow of water from the water collecting pit dangerously, if the air closing of the discharge valve is failed due to a trouble in the valve operating system for example.